Add Portable LibreChat tile (from PR solid#954)

Incorporate @jeswr's PR solid#954 contribution into this PR so that both
apps-list batches land together: a tile for https://chat.solidproject.org/,
a Solid-integrated build of LibreChat that stores chat history in the
user's Pod for portability across compatible clients.

- Re-adds the "Chat" filter option removed in commit f860f46
  (alongside the Liqid Chat removal) now that a working chat app is
  back in the list.
- Uses the a11y-correct markup pattern introduced earlier in this PR:
  native <a href> with descriptive text and rel="noopener noreferrer",
  and both secondary links (LibreChat project site and the solid/LibreChat
  source repo) placed in the sibling <p class="app-source"> outside
  the outer tile anchor so nothing is nested.
- Adds assets/img/logo/librechat.svg (from PR solid#954).

Author: jeswr

apps.html

@@ -32,6 +32,7 @@ <h2 id="app_launcher" property="name">App Launcher</h2>
         <label for="category-filter">Filter by category:</label>
         <select id="category-filter">
           <option value="all">All Categories</option>
+          <option value="Chat">Chat</option>
           <option value="Cooking">Cooking</option>
           <option value="Health">Health</option>
           <option value="Location">Location</option>
@@ -220,6 +221,16 @@ <h3>SolidFocus</h3>
           <p>Manage your tasks and notes seamlessly across workspaces and lists, with offline access, Markdown support, and data stored securely in your Solid POD. Built by Noel de Martin.</p>
         </a>
       </li>
+      <li data-name="Portable LibreChat" data-category="Chat">
+        <a href="https://chat.solidproject.org/">
+          <div class="tile-header">
+            <img alt="LibreChat logo" src="/assets/img/logo/librechat.svg"/>
+            <h3>Portable LibreChat</h3>
+          </div>
+          <p>A build of LibreChat — an open-source AI chat platform that unifies conversations across providers like Anthropic, OpenAI, and Azure — with Solid integrated so that your chat history is stored in your Solid Pod, making your AI conversations portable across compatible clients.</p>
+        </a>
+        <p class="app-source">Upstream project: <a href="https://www.librechat.ai/" class="external-link" rel="noopener noreferrer">librechat.ai</a>. Source code on <a href="https://github.com/solid/LibreChat" class="external-link" rel="noopener noreferrer">GitHub (solid/LibreChat)</a>.</p>
+      </li>
       <li data-name="TiredBike" data-category="Travel">
         <a href="https://tired.bike/">
           <div class="tile-header">